Photothermographic elements have been commercially available for a number of years and are found in various technological formats. The most successful photothermographic systems are those based on the technology disclosed in U.S. Pat. No. 3,457,075. Here it was taught to intimately associate light insensitive organic silver salts with light sensitive silver halide grains in the presence of a developer for silver ions. This intimate association was referred to as having the two silver components in catalytic proximity. This condition of catalytic proximity was first achieved by directly halidizing light insensitive silver organic salts, although it has been subsequently found that catalytic proximity could be achieved by precipitating the organic silver salt in the presence of preformed or coprecipitated silver halide (e.g., U.S. Pat. No. 3,839,049). Three essential ingredients, organic silver salt, silver halide, and developer, were combined in a binder to form a light sensitive, thermally developable imaging element. Subsequent work (e.g., U.S. Patent Application Ser. No. 666,350 filed Mar. 12, 1976) has found that the image silver source material (a material which can be reduced to silver), previously limited to organic silver salts, may also include complexes of any silver salt where the coordinating compound has a gross stability constant of between 4.50 and 10.00 with silver ion. The silver salt may be organic or inorganic with such a system.
A significant limitation in the general utility of these photothermographic systems which use silver halides as the sensitive component has been their lack of speed (i.e., the requirement of relatively high energy for image exposure) and image stability after development.